The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs.
On the other hand, such scaling down process increases the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed. For example, a silicon-on-oxide (SOI) substrate has been introduced to replace a bulk substrate. The SOI substrate has higher operating speed and provides better electrical insulation. In the manufacturing process of the devices in the SOI substrate, further improvements are constantly necessary to satisfy the performance requirement in the scaling down process.